Disposable articles are typically produced at high speed using automated machinery that combine polymer films, absorbent fiber, cover sheets and other components with adhesive materials at high speed resulting in useful articles. In such production, hot melt adhesives are typically extruded and applied at high speeds and at high temperatures (typically about 110° C. through about 280° C.) directly onto a non-woven web, a polymer film, or another flexible component of the final disposable article object. Often a polymer film such as a polyester, polypropylene or polyethylene film is used with the hot adhesive. The film may be combined with an absorbent batt, a non-woven fabric, a tissue, a secondary film or anther fabric absorbent material, etc. using the hot melt adhesive.
Hot melt adhesives can be applied to the surface of the target layer with a variety of techniques including spray techniques or contact techniques such as multidot, multiline, etc. The spray techniques can form spray patterns and randomly oriented lines. Preferably, the hot melt adhesive is used for laminating layers of polymer, non-woven tissue, absorbent batting, cover layer, etc. into a final article. The adhesive can also be used in attaching an elastic material to a sheet-like substrate wherein during elastic attachment, substantial lamination of the structure can occur in a sophisticated assembly technique. In general purpose construction of disposable articles, the adhesive must be compatible with a wide variety of materials. The adhesive must be applied to a variety of substrates under a variety of conditions of time, temperature, add-on amount and manufacturing step. As such, a general purpose adhesive used for such construction must obtain a useful viscosity, typically 2000-8000 cP or 2000-16,000 cP, at the temperature at which the adhesive is applied to a substrate. Adhesive application temperatures are typically above about 120° C. and are typically in the range of 135°-210° C.
Elastic and/or elastic members are typically adhered to a substrate in a disposable article using hot melt application equipment. In the construction of disposable diapers, for example, the elastic is attached typically to the polyolefin substrate using hot melt spray-on equipment in which the adhesive is sprayed onto the polyolefin in a useful, typically overlapping circular pattern. The adhesive is used in an add-on amount from about 5 to about 30 g-m−2. The typical application temperature for the adhesives typically ranges from about 120° C. to about 210° C. Elastic members may be used to seal a leg opening, a waist opening or to obtain a useful contraction of the polyolefin film in other portions of the disposable article.
Typically, the elastic banding is stretched prior to or after contact with the polyolefin backing. Once the elastic banding is stretched and in place with the polyolefin, the adhesive is sprayed on, cooled and the elastic is permitted to relax, creating a gathered polyolefin sheet having substantial flexibility. After the banding is attached to the polyolefin sheet, the elastic can be stretched substantially up to 300% elongation before reaching the elastic limit.
In a preferred mode in attaching elastic materials to one or more substrates, the adhesive must exhibit high resistance to creep. In other words, the elastic material fixed in place by the adhesive, when placed under stress typical in either manufacture or use of the article, should not move substantially from its desired position on the surface of the material. Further, the elastic must not become partially or fully detached from its place of application.
Hot melt adhesives have been formulated for use in attaching elastic materials to one or more substrates. For example, Vaughan et al. (U.S. Pat. No. 6,531,544) disclose a hot melt adhesive suitable for bonding elastic to nonwoven, that further exhibits stress resistance in the presence of lotion on a surface. Zhou et al. (U.S. Pat. No. 6,774,069) disclose compositions of atactic polypropylene and isotactic polypropylene suitable for bonding non-woven elastic composites that exhibit improved bond strength compared to conventional hot melt adhesives. Sambasivam, et al. (U.S. Pat. No. 6,391,960) disclose a hot melt adhesive formulation that is an endblock resin combined with a radial or linear SBS copolymer suitable for use as a construction and elastic attachment adhesive in disposable products. Wang, et al. (U.S. Pat. No. 6,329,468) disclose a hot melt adhesive polyolefin formulation exhibiting good adhesion in elastic attachment applications with nonwoven disposable articles, having low melt viscosity, good heat stability, and oil resistance. Faissat, et al. (U.S. Pat. No. 6,582,762) disclose a polyolefin based hot melt adhesive particularly suitable for spraying applications. McGee et al. (U.S. Pat. No. 6,084,029) disclose a grafted polyolefin hot melt adhesive that does not employ a tackifier, and which exhibits good bonding properties to polar substrates.
Other adhesive formulations have been contemplated using polyolefins. For example, Ikeda, et al. (U.S. Pat. No. 6,949,298) disclose a thermoplastic resin composition comprising a styrene-hydrogenated diene block copolymer, and a second thermoplastic resin that is preferably a polyolefin, that has the desirable property of being capable of reacting with a boron-containing compound via residual unsaturation of the diene copolymer.
Other adhesive applications of polyolefin-based materials include the disclosure in Futugawa, et al. (U.S. Pat. No. 6,753,053) of a laminated film wherein a polyolefin provides adhesion between layers of the film using a coextrusion inflation method. Mueller, et al. (U.S. Pat. No. 6,403,231) disclose a nanocomposite laminated multilayer sheet that is thermoformed e.g. using extrusion techniques, where one or more layers comprise a polyolefin that provides adhesion between layers of the sheet.
Polyolefin compositions modified with maleic acid groups are also known. The technique of grafting maleic anhydride onto polyethylene and polypropylene was initially disclosed by Ames (U.S. Pat. No. 4,358,564).
Further, Mussig (U.S. Pat. No. 6,319,353) discloses a pressure sensitive composition comprising a maleic acid anhydride modified polyolefin copolymer. Godfrey (U.S. Pat. No. 5,763,516) discloses a polyolefin grafted with maleic anhydride as one component of a hot melt adhesive, along with a wax. Herridge, et al. (U.S. Pat. No. 5,660,922) and Leonard et al. (U.S. Pat. No. 5,589,122) disclose a pressure sensitive adhesive layered construction that can employ a maleic anhydride modified polyolefin as a layer disposed between a backing and the pressure sensitive adhesive layer. Mattson (U.S. Pat. No. 5,439,974) discloses an adhesive that employs a polypropylene polymer and a grafted ethylenically unsaturated carboxylic acid or derivative grafting monomer such as maleic anhydride. Amici et al. (U.S. Pat. No. 5,378,758) discloses a hot melt adhesive composition that may employ a copolymer of, among other monomers, propylene and maleic anhydride as one component of the formulation. Kiang et al. (U.S. Pat. No. 5,367,022) disclose a maleic anhydride grafted polypropylene that is useful in an adhesive composition. Ohmae et al. (U.S. Pat. No. 5,075,382) disclose an adhesive composition employing a blend of an ethylene/(meth)acrylic acid ester/maleic anhydride copolymer with a silane-modified ethylene copolymer. Lee (U.S. Pat. No. 5,035,457) discloses a low melt index, tackifier-free polyethylene grafted with maleic anhydride that is part of an extrudable adhesive formulation. And Stuart et al. (U.S. Pat. No. 4,719,260) disclose a polypropylene based hot melt adhesive formulation wherein the tackifier resin is maleated.
Currently, the commercially implemented adhesives for elastic attachment in diaper manufacture are sold by H.B. Fuller Company and Bostik under the product names HL-1484 and H-2525-A, respectively. In large part, these construction and elastic attachment adhesives are made from styrene isoprene styrene or styrene butadiene styrene ABA block copolymers combined with plasticizers, extending oils, tackifiers, fillers and other components to form a useful locus adhesive.
We have found in our work that currently available adhesives are not optimal in one or more properties including open time, viscosity at application temperature, or resistance to creep. Accordingly, a substantial need exists for adhesive compositions having improved open time, viscosity at application temperature, and creep resistance; similarly, a need exists for improved disposable article constructions employing such an improved adhesive.